The present invention relates to a press felt for use in a papermaking machine, and to a method of manufacturing the press felt, which is of the type comprising a woven base fabric which is made of yarn material and is endless in the machine direction (i.e. in the running direction of the press felt in the papermaking machine), and one or more layers of fiber material arranged on the base fabric.
The term "endless base fabric" as used herein and in the following relates to a base fabric which is closed during operation. The term "endless" should, in particular, be considered also to include the case where the base fabric can be opened across the machine direction for mounting in a papermaking machine, and subsequently joined together by means of a locking seam.
The "fabric of yarn material" as mentioned above may in particular be some type of woven or knitted fabric, and the term "fiber material" includes all types of batt layers and %he like that can be used in a press felt.
Currently, base fabrics for press felts are manufactured mainly by tubular weaving technique which is known to those skilled in the art and according to which the fabric is made in the form of a tube or a hose-pipe and the weft threads are alternately passing into an upper warp thread layer (upper cloth) and a lower warp thread layer (lower cloth). The extent of this "tube" in the transverse direction of the weaving loom thus corresponds to half the length of the final base fabric. The width of the base fabric is determined by the weaving length.
This known technique suffers from the following shortcomings:
1. The length of a tubular-woven base fabric is determined by the reed width in the weaving loom. A tubular-woven base fabric thus has a given length which
cannot be modified afterwards and which therefore, during the very weaving operation, must be adjusted to precisely the papermaking machine in which the press felt is to be mounted. Hence, the base fabric and thus the press felt cannot be manufactured and kept in stock in large series, but must be manufactured to a specific order. This extends the delivery time and means low degree of utilisation of the weaving equipment.
2. When adapting a weaving-loom to a longer base fabric, new warp threads must be entered, which not only takes time, but also involves problems in terms of quality, since after such an adaptation of the weaving loom, it is necessary to weave one length of useless base fabric (junk cloth) before the new warp threads will have the correct tension in the fabric.
3. The weaving looms must be given a considerable width, preferably over 20 m to permit tubular weaving of all current lengths of base fabric. The weaving looms therefore become both bulky and expensive.
4. Weaving short base fabrics in a wide weaving loom means low degree of loom utilisation, as well as waste of thread because of the warp threads that are not used, but yet must be fed during the weaving procedure.
5. It is difficult to achieve uniform tension level in the relatively large number of warp threads.
6. At the loom edges where the weaving is directed in either cloth, it is difficult to reach the average yarn density, resulting in irregularities at the loom edges. With such irregularities there is a risk of inducing vibrations during operation and also markings in the paper web.
Hence, there is a current need to solve the problems related above.